Gas turbines are used in many fields for driving generators or driven machines. In this case, the energy content of a fuel is used for producing a rotational movement of a turbine shaft. For this, the fuel is combusted in a combustion chamber, wherein compressed air is fed from an air compressor. The operating medium, under high pressure and under high temperature, which is produced in the combustion chamber as a result of combusting the fuel is directed in this case through a turbine unit, which is connected downstream to the combustion chamber, where it expands, performing work.
For producing the rotational movement of the turbine shaft, in this case a number of rotor blades, which customarily are assembled into blade groups or blade rows and drive the turbine shaft via an impulse transfer from the operating medium, are arranged on this turbine shaft. For flow guiding of the operating medium in the turbine unit, moreover, stator blades, which are connected to the turbine casing and assembled to form stator blade rows, are customarily arranged between adjacent rotor blade rows.
The combustion chamber of the gas turbine can be constructed as a so-called annular combustion chamber, in which a multiplicity of burners, which are arranged around the turbine shaft in the circumferential direction, lead into a common combustion chamber space which is enclosed by a high-temperature-resistant surrounding wall. For this, the combustion chamber in its entirety is designed as an annular structure. In addition to a single combustion chamber, provision may also be made for a multiplicity of combustion chambers.
A first stator blade row of a turbine unit as a rule directly adjoins the combustion chamber and together with the directly following rotor blade row, as seen in the flow direction of the operating medium, forms a first turbine stage of the turbine unit to which further turbine stages are customarily connected downstream.
The stator blades in this case are fixed in each case on a stator blade carrier of the turbine unit via a blade root which is also referred to as a platform. In this case, the stator blade carrier can comprise an insulating segment for fastening the platforms of the stator blades. Between the platforms—which are arranged in a spaced apart manner in the axial direction of the gas turbine—of the stator blades of two adjacent stator blade rows, a guide ring is arranged in each case on the stator blade carrier of the turbine unit. Such a guide ring, by means of a radial gap, is at a distance from the blade tips of the rotor blades of the associated rotor blade row which are fixed on the turbine shaft at the same axial position. As a result, the platforms of the stator blades and the guide rings, which in turn are possibly of a segmented construction in the circumferential direction of the gas turbine, form a number of wall elements of the turbine unit, constituting the outer limit of a flow passage for the operating medium.